1. Field of the Invention
This invention relates to x-ray lithography and metrology systems, and more particularly to alignment or detection systems for that purpose.
2. Description of related art.
In lithography, it is known to employ visible light to perform measurements in alignment systems. However, when measurements are to be made in x-ray technology, the limits of conventional optical measurements are exceeded. These limits are in general, caused by the fact that systems using visible optics are less accurate than is required because of wavelength limitations.
U.S. Pat. No. 4,016,416 of Shepherd et al, for "Phase Compensated Zone Plate Photodector" shows a zone plate with a photodetector mounted on the opposite face.
U.S. Pat. No. 3,984,680 of Smith for "Soft X-Ray Mask Alignment System" shows an x-ray mask alignment system with x-ray fluorescence detectors mounted on the mask which measure the x-ray fluorescent signal which provides a low intensity output as compared with an electron flux.
U.S. Pat. No. 4,614,433 of Feldman for "Mask-to-Wafer Alignment Utilizing Zone Plates" shows mask to wafer alignment using zone plates illuminated by light during alignment.
In accordance with this invention, a method and apparatus is provided for aligning an x-ray lithography system including an x-ray mask and a work piece with an alignment mark, including the steps as follows:
a) including means on the x-ray mask for focussing the x-ray beam on the work piece such as a zone plate or grating,
b) directing x-rays through the means for focussing at the alignment mark for detecting when the lens or grating is aligned with the mark by emission of photoelectrons generated by the work piece in response to the x-rays and detecting the change of current when the x-ray beam crosses a feature on the alignment mark.
Preferably the alignment mark comprises an etched slot or a metal feature.
Further in accordance with this invention, an apparatus and a method are provided to improve the detection capabilities of a metrology system for measuring a work piece in connection with a plurality of fiducial marks forming an array on the work piece, comprising
a) providing an x-ray source,
b) providing a means for focussing such as a zone plate lens or a grating on an x-ray transparent substrate,
c) directing x-rays through the zone plate lens to a first one of the fiducial marks for detecting when the lens or grating is aligned with the mark by emission of photoelectrons generated by the work piece in response to the x-rays and detecting the change of current when the x-ray beam crosses a feature on the first one of the fiducial marks,
d) a laser interferometrically controlled table that determines the position between two of the fiducial marks in the array of marks. previously defined on the work piece.